The information hidden in the shape of the cosmic microwave background spectrum

Cosmic microwave background (CMB) is the primordial radiation created in the 'beginning' of the Universe which has cooled down to 2.725 Kelvin today and observable in microwave part of the electromagnetic spectrum.  The Universe in the distant past was very hot and dense and in complete thermal equilibrium. The laws of thermodynamics imply in this case that the spectrum of the photons must be described by the Planck/blackbody spectrum with only one parameter, the temperature. Subsequently as the Universe cooled with expansion, the physical rocesses responsible for maintaining the equilibrium became less efficient and it was possible for the spectrum of the CMB to be influenced by the local physics in the primordial plasma. As a result, the spectrum of the CMB we observe today is expected to contain deviations from a perfect blackbody spectrum. CMB being the oldest radiation in the Universe (hence the 'background' in the name) therefore contains information about fundamental physics operating in the early Universe. I will give an overview of how the CMB spectrum (including deviations from a blackbody) is created and what we will learn about fundamental physics from future experiments designed to make a precise measurement of the CMB spectrum.